A regenerated collagen fiber, as a protein fiber, is close to human hair in various properties, and accordingly is suitably used as a raw material for artificial hair. High aesthetic properties such as color appearance and texture are demanded in a fiber for use as a raw material for artificial hair.
Protein fibers are generally colored according to a dyeing method. As the dyeing method, there is used a dyeing method comprising immersing protein fibers in a dye aqueous solution in a temperature range of 70 to 100° C.
Specifically, for instance, D1 recites a dyeing method comprising: immersing wool in a dye aqueous solution containing an enzyme or a like compound for enhancing the dye leveling; and boiling the solution at 100° C. for 60 minutes.
D2 recites a method for dyeing protein fibers such as wool, cashmere wool, and silk threads, with use of a specific treating agent, in a temperature range of 70 to 90° C., which is lower than a conventional dyeing temperature. In Examples of D2, there is disclosed an example, wherein wool is treated with a specific treating agent, and the treated wool is dyed at a dyeing temperature of 85° C.
As described above, in the conventional general protein fiber dyeing method, a high-temperature treatment over 70° C. has been required to allow the protein fibers to sufficiently exhaust the dye, even in use of a specific treating agent.
In the case where regenerated collagen fibers are dyed by a dyeing method such as requiring a high-temperature condition over 70° C., the regenerated collagen fibers may shrink.
In order to solve the above drawback, the inventor has tried to dye regenerated collagen fibers at a temperature of 70° C. or lower. However, in the case where the dyeing temperature is low, chemical reaction of regenerated collagen fibers and a dye is insufficient, which may lower the dye fastness. Also, in the case where regenerated collagen fibers having low dye fastness is used as artificial hair, the dye in the regenerated collagen fibers may be transferred to a garment in contact with the regenerated collagen fibers by way of water such as sweat.
In view of the above, as a method for coloring regenerated collagen fibers, a method comprising dispersing a pigment such as carbon black for coloring in a solution spinning process for producing regenerated collagen fibers has been a solely practical method. However, in the coloring method using a pigment, a possible color range obtained by the coloring has been limited to achromatic colors such as black and gray, and it has been difficult to obtain vivid color appearance on chromatic colors such as red, yellow, blue, and purple, as well as deep black or the like.
D1: Japanese Unexamined Patent Publication No. Hei 2-216282
D2: Japanese Unexamined Patent Publication No. Hei 7-126988